1. Field of the Invention
The present invention relates to a printing apparatus and a printing method and, more particularly, to control of a carriage motor having periodical torque fluctuations.
2. Description of the Related Art
Recently, demand is growing for higher image qualities of printing apparatuses. Measures to increase image quality include increasing the printing medium conveyance precision, printhead printing precision (for example, for an inkjet printer, the inkjet discharge amount and discharge timing), and the operation precision of a carriage on which a printhead is mounted.
Of these measures, here attention is paid to the carriage operation precision. In general, an inkjet printer or the like simultaneously performs carriage operation control and printhead printing control because the printhead prints while the carriage operates. Thus, the carriage operation precision based on a control signal from a controller influences the printing precision.
In most cases, the carriage uses a motor as a driving source. The driving force of the motor is generally transmitted by engaging a gear-shaped pulley attached to the motor shaft with a belt to which the carriage is attached. A DC brushless motor is often used as the motor, and periodical torque fluctuations (cogging torque) are generated due to a structural factor. Owing to the torque fluctuations, the rotation speed of the motor fluctuates, and the carriage velocity becomes unstable, resulting in poor printing precision.
To solve this, Japanese Patent Laid-Open No. 2005-178334 discloses a technique for suppressing velocity fluctuations. More specifically, a periodic signal is generated to cancel velocity fluctuations caused by the cogging torque, and motor driving is controlled in accordance with the signal.
In Japanese Patent Laid-Open No. 2005-178334, the periodic signal is generated based on the carriage position. The relationship between the motor rotation position and the carriage position may change when, for example, a foreign substance collides with the carriage to generate tooth jumping between the belt and the pulley. In this case, the relationship between the periodic signal timing and the motor rotation position deviates from an optimum state, velocity fluctuations cannot be appropriately canceled, and the periodic signal needs to be generated again. Also, in this case, the user cannot use the printing apparatus while parameters are identified, generating the downtime of the apparatus.